The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a structure of a programmable read only memory (PROM) with a poly-silicon fuse of the emitter follower type and a method of manufacturing the same.
With more multifunction and higher operation speed of recent microprocessors, there are increasing demands of larger capacity and higher speed of the PROM. The bipolar type PROM is inferior to the MOS type PROM in that the data once written into the bipolar type PROM can not be corrected. Nevertheless, it is superior to the latter in that the access time is much shorter than that of the latter and it has a higher reliability.
The writing method of the bipolar type PROM is categorized into a fuse melting method (a diode junction type or an emitter follower type) and avalanche induced migration (AIM) method, depending on the cell structure. The fuse melting method is disclosed in Japanese Patent Disclosure (KOKAI) No. 48-97457, for example. In this device, the base contact hole and the emitter contact hole must be provided with a sufficient separation. Accordingly, the base contact hole occupies a larger area in the cell area, so that the improvement of an integration density of the device is hindered. Further, a parasitic capacitance formed between a word line and collector-base junctions grows to an extent that it is not negligible, thereby to prevent the improvement of the operation speed of the device.